1. Field of the Invention
This invention relates to a novel solid catalyst component suitable to gas phase polymerization, particularly to gas phase copolymerization of .alpha.-olefins, a catalyst for .alpha.-olefin polymerization obtained by combining at least the above component with an organoaluminum compound and a process for producing the same.
More particularly the present invention relates to the above-mentioned solid catalyst component characterized in that it is a hollow particle having a shape close to sphere, a uniform particle size and a vacancy therein, a catalyst for .alpha.-olefin polymerization using the catalyst component and a process for producing them.
2. Description of the Related Art
In the production of .alpha.-olefin polymers, when the solid catalyst component used therein and the resulting polymer particles have a non-uniform particle size and are in the form of fine particles, handlings such as separation, drying, carrying, etc. thereof become difficult and also operational troubles due to scattering, adhesion, formation of mass inside the apparatus occur; such matters become a cause of productivity reduction and quality problem. It has been well known that disadvantages in the production process due to handling of such a solid catalyst component and polymer particles become more apparent in the production of .alpha.-olefin polymers produced by gas phase polymerization.
The present inventors have previously presented a process for producing polyemr particles having a small average particle diameter, a shape close to sphere and a narrow particle size distribution (Japanese patent application laid-open Nos. Sho 56-110,707/1981, Sho 56-120,712/1981, etc.; the inventions of these applications will hereinafter be often referred to as "previous inventions"). The solid catalysts used in these processes have such specific features that they have notably improved storage stability and thermal stability as compared with those of the prior catalysts of the same kind and also a high polymerization stability, and further, polymers obtained by using such catalysts have such specific features that they have a high bulk density and a high crystallinity of polymers, and furthermore since the polymers have a shape close to sphere and a uniform particle size, they are advantageous in the aspect of production and handling of polymers.
As described above, the prior inventions found by the present inventors have overcome the drawbacks of the prior art, but in the case of gas phase polymerization, particularly in the case of production of .alpha.-olefin copolymers by gas phase polymerization, solvent-soluble polymers which can be separated in the case of slurry polymerization, are contained in the polymer particles as an adhesive component; hence a production-operational problem accompanying the inferiority in the powder fluidity represented by powder characteristics such as increase in the angle of repose of polymer powder, notable change in the bulk density before and after tapping, etc. and also a quality problem caused thereby and the like problems have been liable to be raised. Accordingly it has been necessary to overcome these problems.
In general, as to powder fluidity, a correlationship is observed between the average particle diameter and the powder fluidity in the case of spherical particles having a uniform particle size, and the powder fluidity is improved in proportion to increase in the average particle diameter ("Powder", pages 740-744, coedited by Kiichiro Kubo, Eiji Minawata, Yuzo Nakagawa and Kyohhachiro Hayakawa).
In view of the above-mentioned knowledge, it may be considered that by increasing the size of the particles of the solid catalyst component for .alpha.-olefin polymerization catalysts, the average particle diameter of the .alpha.-olefin polymer particles obtained by using the resulting catalyst may be increased to thereby improve the powder fluidity of the polymer.
However, when the solid catalyst component having a particle size required for satisfying the improvement in the fluidity of the .alpha.-olefin polymer particles is used, the following various problems are raised, that is, the following disadvantages relative to productivity and qualities occur:
With regard to the catalyst performance, reduction in the polymer yield per the unit catalyst quantity; with regard to the polymerization activity, stereoregularity, etc., occurrence of deterioration of catalyst with lapse of time during the polymerization; and with regard to the process, reduction in the polymer productivity per the polymerization apparatus, increase in the load applied in the post-treatment process for making harmless the catalyst component contained in the polymer, and increase in the energy required when additives, etc. are caused to be melt-kneaded into the polymer in the granulation process, etc.
The present inventors have made extensive research in order to find a catalyst component which can overcome the above-mentioned disadvantages brought by the increase in the particle size of the solid catalyst component at the time of producing .alpha.-olefin polymers having a good powder fluidity by gas phase polymerization, and at the same time which can maintain the superior specific features of the catalysts in the production processes of .alpha.-olefin polymers offered formerly by the present inventors. As a result, the present inventors have found a hollowed solid catalyst component having a large average particle diameter, a uniform particle size and a vacancy inside the particle, and a process for producing the catalyst component, and further, when a catalyst obtained by combining the catalyst component with an organoaluminum compound is used, the above-mentioned object can be achieved.
As apparent from the foregoing, the object of the present invention is to provide a hollowed solid catalyst component which can produce .alpha.-olefin polymers having a high stereoregularity and a good fluidity, stably and with a good efficiency in gas phase polymerization, particularly in gas phase copolymerization, a catalyst for .alpha.-olefin polymerization using the above solid catalyst component and a process for producing the above catalyst component.